Aeration of liquids



Ri l.

P htented Sept. 15, 1931 Qumran stares v HARMON n.

A EBATION No Drawing Application filed July 13,

p This invention pertains specifically-to the means of aerating solutions by gases which contain solid particles, such as flue dust, in suspension. It will 'be more clearly illustrated by briefly describing the steps of a process in which it is employed.

In the leaching of, certain types of ores, it is desired to produce ferric sulphate and sulphuric acid, by treating ferrous sulphate '1 solution with sulphur dioxide and air, a

from experience in the field of flotation that a porous bottom cell would not'be. a feasible device for aerating solutions with roaster gas because of inevitable clogging of the interstices of the porous medium by solid particles, such as flue dust, suspended in the gas. Only by cleaning the gas to an extreme degree was it deemed possible to aerate solutions with roaster gas through a porous medium of fine texture without building up back pressure to an objectionable extent. Such methods of gas cleaning as scrubbing with water, use of filters, bag houses or electrostatic precipitators are costly and complicate the process. Even-by the use of such devices it was considered, previous to my discovery, thatthe pressure on the porous medium would accumlate so as to make blowing of roaster gas through porous media impracticable if any appreciable amount of dust were present. In fact, some modern flotation plants scrub the air with water to remove dust before blowing it into porous bottom cells.

I have found, however, thatunder proper conditions not only may roughly cleaned 50 roaster gas be blown through certain porous medla of fine texture, but that the bubbles are szasn mama orrica 192?. Serial m. 205,529. r

more uniformand smaller in size because of the pressure ofsolids in the gas, thereby improving the metallurgical results.

The following. description illustrates my observations: 7 a I 1. A thimble type of aerator was constructed of closely woven woolen cloth and connected at the bottom of a column of solution.

was blownin and the aressure on the M fabric noted. Finely divided calcine was then F3 introduced w th the air for several hours and the pressure and bubble size observed. Upon the application of the dust the pressure rose a few tenths of a pound and then remained M constant, the bubbles becoming smaller and It v more uniform in'size and distribution. The rate of'addition of dust was about 10 times what would be encountered in ordinary plant practice by using roughly cleaned roaster gas. m

By roughlycleaning gas is meant removal J ofonly the portion of the dust that settles readily in cyclone or other simple and inexpensive dust collectors or chambers.

2. Tests were run on various fabrics, using K both single and double thicknesses, by blow- G515 ing fine dust and'air through the fabric into water. Each of these tests was of about 8 hours duration, although many repelit'ions were made on thesame fabric. In-thiscase V the fabrics consisted of closely woven woolen ST.

cloths with felted surfaces, In no case was the increase in-press'ure'due to the dust more than one pound per square inch and itwas ,found that the pressure on the clothsoon reacheda constant value. g 7

' 3. An aerator was constructed of approximately 7 square feet cross section and 6 feet inheight. closely woven woolen fabric, nearly equal in area to the tank, was tightly secureda few inchesabo've the cell bottom. 0 ,(Details of'cell designare not given here as thisjinvention pertains to the basic idea of aeration withdirty roaster gas 'andnot to any 1 specific design of apparatus). "A column F height of liquidof feet was employed, the solution dilute iron sulphate and sulphuric acid. v Pyrite was burned in a multiple hearth roasterto furnisha 'as containin about): ercent sul )hur dioxide. This as was roughly cleaned by passing through ineX- pensive types of dust collectors which caused mechanical settling of the coarser particles and allowed much of the fine dust and fume to pass tl rough the rotary blower which followed the dust collector and forced the gas into the cell through the porous fabric.

The cell was constructed so that solution could be back flushed through the cloth, if necessary, to clean the dust from the under side. However, in the series of about 20 tests which followed, using a single, closely woven blanket of multiple ply weave, no trouble occurred from increase in pressure on the cell blanket, nowithstanding the fact that in some cases the pipes conveying the gas to the cell became nearly choked with dust.

It has been found that dirty roaster gas may be successfully blown through a fabric of small interstices into a solution, thereby producing bubbles of 0.5 to 3 milli-meters diameter, and that the pressure on the fabric soon reaches a constant value. When the proportion of dust in the gas is not too great considerable of the dust is carried through the fabric, especially through the larger 1nterstices. In so doing some of the particles adhere to the fabric, thus partially closing the larger interstices as the greater volume of the dust containing gas obviously passes through the larger openings. This causes a slight increase in pressure which results in the gas being forced through smaller openings than was formerly the case. The net effect is an improvement in distribution of the gas,

smaller bubbles and no necessity for a costly and extensive gas cleaning system. The limits of tolerance as to maximum and minimum proportions of dust relative to gas depend on local conditions, this specification not being confined to any definite percentage of solids in the gas. For best results the cleaning is carried just to the point where most satisfactory gas distribution and bubble size, consistent with low pressure, are attained. In steady operation with clean gas the pores of the fabric tend to become enlarged. The

result would be to increase the bubble size, which is undesirable in this and other processes. but this may be prevented by my meth- 0d of allowing a certain amount of dust to remain in the gas.

My discovery greatly simplifies and cheapens the process of auto-oxidation of ferrous sulphate and sulphur dioxide in the presence of air, because the gas may be blown directly into the ferrous sulphate solution instead of having to use a costly cleaning system or an indirect method of absorption as has been previously proposed.

The method herein described is also applicable to other processes where it is desired to produce fine bubbles in a solution. In some cases it may be advantageous to add a certain amount of dust to the gas to improve the uniformity of distribution and decrease he bubble size.

Having described my invention what I claim and desire to patent is 1. A method of treating solutions with gases, comprising injecting finely divided solids in the gas and then passing the gas containing the solids in suspension into the liquid through a porous medium in contact with the liquid to efiect intimate contact between the gas and liquid said solids being of a size sufficient to only partially clog the pores of the porous medium.

2. A method of increasing the efficiency of a porous medium positioned between a body of under pressure and a body of liquid through which the gas is forced, comprising injecting into the gas solid particles of a size 3. A method of oxidizing a solutionof-ferrous sulphate comprising subjecting gasesi from roasting sulphide ores to a separation treatment to remove only the larger solid particles carried in suspension, then passing the containing the remaining solid particles into the solution, through a porous medium in contact with the solution, the size of the solid particles le t in the gas being of a size relative to the size of the pores in the porous medium so that a partial clogging of the pores will be efiected.

HARMON E. KEYES. 

